Well apparatus and method



June 4, 1968 H. U. GARRETT WELL APPARATUS AND METHOD Filed Sept. 6, 1966 @a ZA F'. Z ffy 2 Sheets-Sheet 1 43 ,sgg

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l IUI NAHI Heffi/y Gaf/'eff j ATTOR YJ United States Patent O 3,386,391 WELL APPARATUS AND METHOD Henry U. Garrett, P.0. Box 35167, Houston, Tex. 77035 Filed Sept. 6, 1966, Ser. No. 577,405 Claims. (Cl. 10S- 233) This invention relates to gas lifting of liquids in a well and more particularly relates to a new method and system for lifting liquids and to a new valve to be used in gas lifting.

It is conventional in gas lifting to unload liquid in a well down to a working level using unloading valves at spaced intervals along the tubing. One popular method of unloading is to set the valves at decreasing pressures in descending order and reduce the casing pressure as the valves are uncovered to permit the several valves to successively close so that the gas will only be injected through one or two valves at a time. This system works Well but with past systems it has required that the casing pressure be maintained below the opening pressure of the lowermost unloading valve during the normal working or operation of the well to prevent opening of unloading valves. This prevents the full utilization of available casing pressure for gas lifting.

In the past there has 'been no simple system available in which these unloading valves could 'be rendered inoperative so that working valves could be operated by casing pressure without opening the unloading valves.

By providing a simple system, method and valve in which the unloading valves are inoperative in response to casing pressure once they are closed by a reducing casing pressure it is possible to set the well up for automatic unloading by metering gas to the casing. The casing pressure will show the closing of each valve so that the actual operation and condition of .the well will be indicated bythe casing pressure.

It is an object of this invention to provide a system, a method and a valve for gas lift in which gas may be metered at a selected rate into the casing while all the unloading valves are in the open position and the well will automatically unload while successively closing the unloading valves in descending order and after the well has unloaded, the casing pressure will automatically return to its maximum pressure and thereafter the well may be worked through working valves at maximum or any other desired casing pressure without the unloading valves reopening in response to casing pressure.

Another object is to provide a method and system of unloading and producing a well by gas lift wherein unloading valves are closed after unloading in response to casing pressure and once closed are not affected by casing pressure to permit operation of working valves at any desired casing pressure.

Another object is to provide a method and system of unloading a well wherein recorded changes in casing gas pressure indicates the closing of unloading valves and wherein the valves that once closed are non-responsive to casing pressure to permit operation of working valves at any desired pressure.

Another object is to provide a method and system of unloading and producing a well by gas lift wherein unloading valves are opened in response to tubing pressure and latched in open position to permit gas lift with casing pressure and are closed in response to casing pressure and once closed, are non-responsive to casing pressure to permit operation of working valves at any desired pressure.

Another object is to provide a valve which opens in response to tubing pressure, is automatically latched in open position and is closed in response to casing pressure.

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Another object is to provide a valve which is opened in response to an increasing tubing pressure, is automatically latched in open position so long as casing pressure is above a selected value and is closed in response to a reducing casing pressure.

Another object is to provide a valve as in the preceding object with a pressure responsive internal valve permitting multiple point injection through unloading valves.

Other objects, features and advantages of the invention will be apparent from the drawings, the specification and the claims.

In the drawings, wherein like reference numerals indi-cate like parts and wherein illustrative forms of this invention are shown:

'FIG. l is la schematic view through a well in vertical cross-section illustrating this invention;

FIGS. 2a and 2b show partially in elevation and partially in vertical cross-section a valve constructed in accordance with this inventionfwith FIG. 2b being a continuation of FIG. 2a;

FIG. 3 is a fragmentary view partially in elevation and partially in cross-section illustrating a modified form of the valve of FIGS. 2a and 2lb;

FIG. 4 is a view partially in elevation and partially in vertical cross-section illustrating a further modified form of this invention;

FIG. 5 is a fragment `of a chart illustrating pressure conditions in the casing of a well unloaded in accordance with this invention; and

FIG. 6 is a fragmentary View partially in elevation and partially in vertical cross-section illustrating the parts of the valve of FIGS. 2a and 2b in a position in which the valve member is latched in open position.

In accordance with this invention a valve is provided which is opened in response to tubing pressure and automatically latched in place in response to the valve moving to open position. The valve is closed in response to casing pressure which triggers the latch mechanism and permits the valve to close.

In the preferred form shown in FIGS. 24a and 2b, casing pressure is raised to a value at which the latch tripping mechanism is inoperative and tubing pressure to a value at which the pressure differential across the valve member moves it to open position to permit automatic operation of the latch. Then a reduction in tubing pressure permits the valve to be used for unloading with casing gas in the customary manner. When the casing pressure reduces this actuates the latch tripping mechanism and the valve moves to close position. As shown, an additional pressure responsive valve lmay be provided for multiple point injection during working of the Well. After the well is unloaded, it is gas lifted in the conventional manner through any conventional pressure responsive valve and as casing pressure has no effect on the unloading valves, any desired casing pressure may be used.

Referring now in detail to the drawings, there is shown in FIG. 1 a well having a casing 10 perforated at 11 at the producing formation.

A tubing 12 is provided in the casing and the tubing casing annulus may be closed adjacent its lower end by a suitable packer 13. Gas lift valves 14 are provided at spaced points along the tubing to provide for unloading and working of the well. While only two valves are shown it will be understood that the number of valves vary with the installation and are usually much more numerous than the two shown.

At the surface a means is provided for injecting lifting gas into the casing 10 at a controlled rate. This means is illustrated schematically by the pump 15 and the orifice 16. Any suitable source of gas and any suitable method of regulating the rate at which the gas is introduced into the casing may be utilized.

The gas lift valve 14 has a housing provided by a nosepiece 20, a lower sub 17, a valve cage 18, an adapter 19, a bellows housing 21, a dome section 22, and an upper closure 23.

The valve illustrated is of the wireline type and thus includes the lower packer section 24 and the upper packer section 25. The invention may be practiced with any type of system such as the conventional system in which the valves are permanently installed as distinguished from removable by wireline.

A flowway is provided through the valve and includes the inlet ports 26, 27 and 28, the accumulator chamber 29, the bore 17a and 17h through the lower sub 17 and passageways 30 through the nosepiece 20.

Flow through the above-dened flowway is controlled by a cooperative valve member and valve seat. The valve member provides a pressure responsive area on which tubing pressure may act to move the valve member to open position. The valve seat is provided by the bore 17b and a pair of spaced seals such as O-rings 31 and 32. The valve member is provided by the generally tubular member 33 which is slidable within the bore 17 b and cooperates with the seals 31 and 32 to prevent flow between the Valve member and the bore 17b.

The valve member 33 has a bore 34 extending therethrough and a port 35 between the bore 34 and the exterior of the valve member. Thus when the valve member is in close position as shown, no How occurs through the port 35 as it is straddled by the seals 31 and 32. With the valve member in its upper position, port 35 communicates with the chamber 29 and uid flows through the valve past the back-check valve indicated generally at 36 and out through the passageways 30.

In accordance with this invention, latch means is provided for latching the valve member 33 in open position. This latch means preferably functions automatically upon movement of the valve mem-ber 33 to open position. This latch means is provided by cooperating dogs and a groove into which the dogs move when the valve is in fully open position.

In the FIG. 2 form of invention, the groove is provided by the bore 19a, the flange 37 immediately above this bore and the upper end 18a of the valve cage 18. A plurality of dogs provided by balls 38 cooperate with this groove to =hold the valve member in open position.

The latch balls 38 are carried on a valve stem connected to the valve member 33. This stern includes a differential valve housing 39, an upper seat 41, and ball carrying sleeve 42. As shown, the sleeve 42 has holes 43 therein in which the balls 38 are positioned.

The balls 38 are urged to extended position by a plunger 44 which is urged upwardly by the spring 4S. The plunger 44 has a reduced diameter section 44a and an inclined wall section 44b which connects with the large diameter section 44C of the plunger. With the parts in the position shown in FIG. 2a, the small diameter section 44a of the plunger permits the balls to be retracted and to lie between the plunger and the bore through the Valve cage 18. When the valve moves to its open position the balls are free to move outwardly under the influence of the incline wall 44b and spring 45 to the position as shown in FIG 6 in which they reside within the groove. The spring 45 moves the plunger up to position where the large diameter section 44e` engages the balls 38 and locks the valve member in open position.

Means responsive to casing pressure is provided for unlatching the latch assembly. In the form shown, this unlatching means is responsive to casing pressure and more particularly to a reduction of casing pressure below a selected value. The release lmeans is provided lby a release plunger 46 which is engageable with the plunger 44 as illustrated in FIG. 6 and when the plunger 46 moves downwardly it moves the ball retaining plunger 44 downwardly to a position to which the balls 8 can retract to the relationship shown in FIG. 2b. Any means responsive to casing pressure may be utilized to move the latch release plunger 46 downwardly. In the illustrated form, a dome 47 containing a pressure charge is provided. This pressure dome is closed at its lower end by the bellows 43 which is in turn connected to the stern 49 which carries the latch release plunger 46. From the construction illustrated in FIG. 2a it is clear that as the casing pressure is reduced below a selected value, the pressure in dome 47 expands the bellows 48 which moves the guide pin 49 downwardly carrying with it the latch release plunger 46 to release the latch means.

The guide stem 49 is provided at its upper end with an enlarged portion 49a which functions as a guide and cooperates with the flange 51 on the release plunger 46 to guide the stem 49. A suitable seal 52 is provided in the ange 51 to cooperate with the lower end of the bellows housing 21 and protect the bellows against excess external pressure as is well known to those skilled in the art.

The operation of the valve just described is as follows:

The valves, installed in a string of tubing, will have the main valve in the position shown in FIG. 2b because the ellows 48 will be extended to hold the latch in release position and the weight of the valve member will probably move the main valve to close position. It is of no consequence that the main valve is open or closed under static conditions as the latch mechanism is retained inoperative.

In the form of valve shown in FIG. 2 lboth casing and tubing pressures are increased after the string is run. Casing pressure is increased to a selected value at which the bellows 48 is compressed and the release plunger 46 is moved to an out-of-the-way position to permit the latch f means to function. Tubing pressure is increased to provide a force moving the valve 33 to its upper open position. The relative casing-tubing pressure will depend upon the areas of the valve member exposed to pressure. In the illustrated form the same area is exposed to tubing and the casing pressure and thus tubing pressure would be raised to a value slightly higher than casing pressure to positively move the valve 33 to full open position where the upper end of dog carrier 42 strikes the ange 37 which functions as a stop. As th'e ball release plunger 46 is in its out-of the-way position the plunger 44 forces the balls 38 into extended position where they latch the valve 33 in full open position. At this time the owway through the valve is open and gas lifting may commence therethrough inthe usual manner.

In normal gas lift operations, the back pressure on the tubing would of course be removed and little or no pressure would lbe present in the tubing, except from the hydrostatic head of liquid above the valve or from separators at the surface or the like. Normally the hydrostatic head would be removed yby gas lifting and little or no tubing back pressure would be present.

In closing the valve, the casing pressure is reduced and `as the casing pressure is reduced to a selected value, the bellows 48 under the force of the charge within the chamber 47 expands to move the release plunger 46 downwardly to thereby :move the dog retaining plunger 44 into its position shown in FIG. 2b to permit the balls 38 to retract. At this time the casing pressure will be larger than tubing pressure, and the differential across the valve 33 will move the valve to fully closed position against the stop provided by ange 53 in the lower sub 17.

In accordance with one aspect of this invention it is desirable that in addition to the latch control valve described above, there be provided at or adjacent to each unloading valve, a pressure responsive valve such as a diierential valve. This differential valve may be provided for purposes of multiple point injection and for unloading the well as fully explained in my copending application Ser. No. 540,707 led April 6, 1966. The differential valve may assume any desired form. In the illustrated embodiment, .the upper end 33a of the valve member 33 serves as a seat for cooperation with the differential valve member 54. The differential valve member is urged upwardly by a spring 55 which conventionally will apply approximately a 100 to 150 pound differential across the valve. The upper valve member 56 of the differential valve Will cooperate with the seat provided by the in-turn flange 57. `It will be appreciated that the valve 56 is formed on a cone and terminates in a cylindrical portion 57 which has a fairly close fit with the bore 58 in Which it reciprocates, thus upon the valve 56 moving off of its seat the valve will crack from its seat. Upon this happening the larger area 57 lwill be subjected to casing pressure and the valve will be snapped to full down position.

With the differential valve in the position shown, casing pressure will be exerted across the area of seat 57. The pressure drop is taken through port 59 and tubing pressure is present on tlhe differential valve across the area of the seat 57 and therebelow. This pressure plus the spring 55 holds the differential valve in open position until the back pres-sure provided by the liquid in the tubing has reduced to such a value that its force and the force of spring 55 is overcome by casing pressure on the top of valve 56. When this pressure is overcome valve 56 cracks from its seat and casing pressure is effective on the larger area of piston 57 to move the differential valve down to engage valve member 54 with its seat 33a. The differential valve will again open when the force exerted by the tubing pressure plus that of the spring 55 overcomes the force of casing pressure acting downwardly across the valve seat 33a Referring to FIG. 3 there is shown a form of this valve in which the differential valve is not employed and the seat 33a is closed by a plug 61. Otherwise the valve of FIG. 3 is identical with the valves of FIG. 2a and 2b. The valve of FIG. 3 would be used in those instances where it was not desirable to have an additional pressure responsive valve in the installation. Of course it is apparent that any type of pressure responsive valve could be utilized and it would not be necessary to use the differential valve of FIG. 2b.

By providing a spring to urge the main valve 33 toward open position, the valve of this invention may function as a differential valve. This is shown in FIG. 4. The valve is identical with the valve of FIG. 2b except that the valve member 133 is elongated and secured to an extension 139 which corresponds with the differential valve housing 39 of the FIG. 2b form of the invention. A suitable spring 140 is provided between the upper end of the lower sub 17 and the lower end of the valve stem extension 39 to urge the valve member toward open position.

In operation of the valve of FIG. 4 it is apparent that the spring 140 provides a portion of the force of tubing pressure required with the FIG. 2 form of the invention. As the valve is run into the hole, the valve member 133 is in the open position. Casing pressure will be raised to render the latch release member 46 inoperative. Tubing pressure will also have to be raised to prevent the casing pr-essure from moving the valve member to close positipn against the force of the spring. The combined force of the spring and the force of tubing pressure will position the valve member in open latched position. Thereafter a Ireduction in casing pressure will release the latch and the force of casing pressure being greater than tubing pressure plus the spring will move the valve to close position, when the valve is used in normal gas lift installations. By normal, is meant where casing pressure gradually reduces when a working valve is open down to a selected value at which the working valve is closed. The working valve of FIG. 4 would be closed by a release of the latch mechanism. Thereafter casing pressure would slowly build up in the conventional manner but the valve 133 would remain closed until the combined force of spring 140 and the hydrostatic head of fluid in the tubing exerted a sufficient force to overcome the force of casing pressure on the valve 133 to thus move the valve 133 to open position. Once open it would of course remain open until the casing pressure bleeds down to actuate the latch release plunger 46.

In considering the operation of the system and methods of this invention, the explanation will first be given utilizing the valve of FIG. 3, for simplicitys sake.

A series of unloading valves constructed in accordance with this invention will be run in association with tubing 12. The lowermost valve may be a working valve or it is pointed out that a valve such as shown in FIG. 2a-2b could -be used and in this case the differential valve would provide the working valve.

The lowermost unloading valve, whether or not it would be associated with a working valve, would have a larger port 35 through the valve member 33 than the other valves for a purpose which will appear hereinafter.

With the string in the well, casing and tubing pressures are raised to a value at which all of the bellows 48 are collapsed to withdraw the latch release plungers 46 to inoperative positions. It might be noted that the domes preferably will `be charged with reduced pressures in descending order which for example, may be 25 to 50 pounds differential between each pair of adjacent valves.

With the bellows 48 collapsed, the tubing pressure is raised to a value at which all of the valves are moved to full open position and the latch mechanism latches the valves in full open position.

After the valves are in full open position, the tubing pressure is removed and gas lift is commenced.

Lifting gas is fed into the casing through a rate controlled means such as the orifice 16 so that the valves will all operate automatically. The orifice is sized such that the ow rate through one of the valves, excluding the lowermost valve, is less than the ow rate through the orifice 16. The flow rate through a plurality of the valves would be greater than the ow rate through orifices 16. Preferably the ow rate through two valves would be greater than the flow rate through the orifice 16.

With the relationship defined above, fluid would U-tube until the uppermost valve is uncovered and exposed to casing gas. This casing gas would lift the fluid above the uppermost valve to the surface. In the meanwhile the fluid would continue t0 U-tube and be gas lifted through the uppermost valve until after the second valve is 11ncovered and exposed to the lifting gas. At this time, two valves are uncovered and as their flow rate is preferably greater than the flow rate through the orifice 16, the pressure in the casing will begin to reduce. As this pressure reduces, the dome setting on the uppermost valve is selected so that it will expand the bellows 48 and close the uppermost valve.

U-tubing and gas lifting will continue until the third valve is uncovered and after the third valve is uncovered pressure will again reduce and the number 2 valve will close. This action will continue as successive valves are uncovered until the last or lowermost unloading valve is uncovered. This lowermost valve has a port size which is greater than the orifice 16 and thus after the valve is uncovered and exposed to gas casing pressure will reduce and the lowermost valve will close.

After the closing of the lowermost valve the well is in a condition for normal operation and normal gas lifting may be carried out through any desired form of working valve or valves such as the differential valve shown in FIGS. 2a2b.

Reference is made to FIG. 5 which illustrates an actual installation of five unloading valves. The top unloading valve was set to close at a rack pressure of 550 pounds. The second unloading valve was set at 525, the third at 500, the fourth at 475, and the fifth at 450.

The well was supplied at little under 600 pounds of pressure at a controlled rate and after the second valve was uncovered the press-ure drop indicated at 141 occurred signaling the closing of the uppermost valve. Continued operation occurred until the pressure drop at 142 indicated the closing of the number 2 valve. The drops 143, 144 and 145 indicate the successive closing of the third, fourth and fifth valves. As the nal pressure at closing of the lowermost valve was around 450` pounds, it was apparent that there was no blockage in the well and all of the valves had functioned properly.

To verify proper functioning of the valves, the pressure is permitted to build up to its original value as shown at 146 on the chart. Then the tubing pressure will again be increased to recock all of the valves. Thus, when the casing pressure again reaches its maximum point and all of the valves are in open position, gas is introduced through all of the valves into the tubing. As a large number of ports are opened, the pressure drop is drastic and falls in a smooth curve very rapidly to 450 pounds. This verifies that all of the valves have functioned properly and that there is no blockage of any sort in the system. If there had been a mal-function in the system, this curve in the system would not have been a fast sharp curve but upon encountering liquid which would have to be lifted after upper valves had closed, the pressure curve would have leveled off. The pressure at which it leveled off would have signaled the particular valve which Was in trouble and would assist the operator in remedial work. After the test is completed all valves are automatically closed and pressure returns to about 60() pounds for a normal Working of the well through the working valves.

It is emphasized that the working valves can be operated at any desired pressure and they can particularly be operated at any desired pressure higher than the pressure of any of and particularly the lowermost unloading valve.

From the above it will be seen that the well unloads automatically and needs no attention or clock controls as it will completely unload and come back to operating pressure for either testing or normal operation if desired. For instance, if the test check is not desired the Well will begin normal gas lift operations upon the casing pressure rising to the level to operate working valve.

The operation of the system and the method when the valves of FG. 2b are present in the string is the same as explained above, except that when the pressure conditions in the tubing and the casing are such that the differential valve opens, these valves will open and Will assist in gas lift. When the string is rst run the hydrostatic head in the tubing will be suicient to open all of the differential valves and U-tubing and gas lifting will occur therethrough. As the hydrostatic head is reduced on the uppermost valve down to the differential set pressure, the differential valves will close. Gas lifting will, however, continue through the port 35.

In accordance with my copending application aboveidentified it will be apparent that the ports 35 could be relatively small and all of the dome chambers 47 set at the same pressure. This would leave all of the valves open until the lowermost valve is reached where the larger port would reduce the casing pressure and close all of the unloading valves. In this form the function of the valve 33 would be more to load the differential valves and permit the diierential valves to unload the well in the manner explained in my above-identified copending application.

lt will be appreciated that the presence of the differential valves at spaced points along the string will provide for multiple point injection as a slug of liquid is raised up the tubing and exerts a suflicient pressure on a differential valve to cause it to open.

It might be noted that the back check 36 has a small passageway therethrough which is controlled by the ball 14S and spring 149. The ball is held off its seat to permit pressure from the tubing to be effective on the dilierential valve. However, if a reversal of pressures occurs the velocity of high tubing pressure passing the ball 148 causes it to seat against the action or" spring 149 to stop backflow through the valve.

While it is preferred to size the orice 16 so that after two valves are open a pressure reduction will occur, it is apparent that this sizing could be related to a plurality of valves such as three valves or more as the action Will be the same. The only difference Will be the absence upon the chart of an indication of the individual closing of the next to lowermost valve where three valves are opened before the uppermost valve closes, etc. While closing of each valve after two valves are opened is preferred, more valves being opened before one valve closes only loses the advantage of a pressure indication on the chart of the closing of each individual valve.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof and various changes in the size, shape and materials, as Well as in the details of the illustrated construction, may be made within the scope of the appended claims Without departing from the spirit of the invention.

What is claimed is:

1. A gas lift system comprising,

a casing,

a tubing in the casing,

means for supplying gas to the casing at a controlled rate,

and a plurality of unloading valves at spaced intervals along the tubing; said valves including, a main valve member and valve seat, means responsive to one of tubing and casing pressure for moving the valve member to open position,

means for latching the main valve member in open position in response to said main valve member being moved to open position,

means responsive to the other of tubing and casing pressure for releasing said latching means and moving said main valve member to closed position, and at least one Working valve for Working the well after unloading through said unloading valves.

2. A gas lift system comprising,

a casing,

a tubing in the casing,

means for supplying gas to the casing at a controlled rate,

and a plurality of unloading valves at spaced intervals along the tubing;

said valves including,

a main valve member and valve seat,

means responsive to tubing pressure for moving the valve member to open position,

means for latching the main valve member in open position in response to said main valve member being moved to open position when the casing pressure is above a selected value,

means responsive to a reduction in casing pressure to a value below said selected value for releasing said latching means and moving said main valve member to closed position,

and at least one working valve for working the well after unloading through said unloading valves.

3. A gas lift system comprising,

a casing,

a tubing in the casing,

means for supplying gas to the casing at a controlled rate,

and a plurality of unloading valves at spaced intervals along the tubing;

said valves including,

a main valve member and valve seat,

means responsive to tubing pressure for moving the valve member to open position,

means for latching the main valve member in open position in response to said main valve member being moved to open position when casing pressure is above a selected value,

means responsive to a reduction in casing pressure t a value below said selected value for releasing said latching means and moving said main valve member to closed position when said tubing pressure is below a selected value,

and at least one working valve for working the well after unloading through said unloading valves.

4. The system of claim 3 wherein the lowermost unloading valve has a flow rate greater than the means for supplying gas at a controlled rate.

5. Method of unloading a well having a plurality of spaced unloading valves which are opened and latched in open position in response to tubing pressure and which are closed in response to casing pressure comprising,

increasing casing land tubing pressures to selected values to open all of said valves and latch them in open position,

decreasing tubing pressure and gas lifting liquid in the well by introducing gas through said valves until the well is unloaded,

decreasing casing pressure to close said valves,

and producing the well through a Working valve at any desired casing pressure.

6. Method of unloading a well having a plurality of spaced unloading valves which are opened and latched in open position in response to tubing pressure and which are closed in response to casing pressure comprising,

increasing casing pressure and tubing pressure to selected values to open all of said valves and latch them in open position,

decreasing tubing pressure and gas lifting liquid in the well by introducing gas into the well casing at a controlled rate until after the top two valves are uncovered and exposed to gas to decrease the pressure in the casing to close the top valve,

continuing gas lifting and closing successively lower valves in response to further reduction casing pressure after the valve therebelow is uncovered and exposed to gas until the lowerm-ost valve is uncovered and exposed to gas,

closing the lowermost valve in response to reduction in casing pressure to a selected value,

and thereafter gas lifting said Well through a Working valve at any selected casing pressure. 7. Method of unloading a well having a plurality of spaced unloading valves which are opened and latched in open position in response to tubing pressure and which are closed in response to casing pressure comprising,

increasing casing pressure and tubing pressure to selected values to open all of said valves and latch them in open position,

decreasing tubing pressure and gas lifting liquid in the well by introducing gas into the well casing at a controlled rate until after the top two valves are uncovered and exposed to gas to decrease the pressure in the casing to close the top valve,

continuing gas lifting and closing successively lower valves in response to further reduction in casing pressure after the valve therebelow is uncovered and exposed to gas until the lowermost valve is uncovered and exposed to gas,

closing the lowermost Valve in response to reduction in casing pressure to a selected value,

again increasing casing and tubing pressures to selected values to open all of said valves and latch them in open position,

decreasing tubing pressure and introducing gas into the well casing at a controlled rate until the casing pressure reduces to the selected value at which the lowermost valve is closed,

and thereafter gas lifting said well through a working valve at any selected casing pressure.

8. A gas lift valve adapted for connection to a well tubing comprising,

a housing,

a ilowway through the housing having an inlet communcating with the exterior of said tubing and an outlet in communication with the interior of said tuba valve seat across said diowway,

a valve member cooperative with the valve seat and controlling iiow through the owway,

latching means for locking the valve member in one of open and closed position,

means for actuating the latching means in response to change in pressure conditions at one of the inlet and outlet of said owway,

and means for deactivating the latching means in response to change in pressure conditions at the other of the inlet and outlet of said owway.

9. The valve of claim 8 wherein means are provided urging the valve member toward open position.

10. A gas lift valve adapted for connection to a well tubing comprising,

a housing,

a flowway through the housing having an inlet communicating with the exterior of said tubing and an outlet communicating with the interior of said tublng,

a valve seat across said tdowway,

a valve member cooperative with the valve seat and controlling flow through the flowway,

latching means for locking the valve member in one of open and closed position,

means for actuating the latching means in response to an increase in pressure at the outlet of said owway to a value greater than pressure at the inlet of said rlowway,

and means for deactivating the latching means in response to a reduction in pressure at the inlet of said tlowway to a selected value.

11. The valve of claim 10 wherein the latching means comprises dogs in a valve stern carried by the valve member and a cooperating groove in the housing,

and wherein the means for actuating the latching means includes a two-position movable means for moving the dogs into the groove in one position and permitting the dogs to retract from the groove in the other position.

12. The Valve of claim 10 wherein a owway is provided through the valve member and a pressure responsive valve member and seat control ow through said lastmentioned flowway.

13. A gas lift valve adapted for connection to a well tubing comprising,

a housing,

a flowway through the housing having an inlet communciating with the exterior of said tubing and an outlet communicating with the interior of said tuba valve seat across said owway,

a valve member cooperative with the valve seat and controlling -ow through the flowway,

a valve stem on said valve member,

a groove in said housing,

dog means carried by the valve stem and positioned to register with said groove when the valve member is in one of open and closed position,

means movable between two positions one of which holds said dogs in said groove and the other of which permits the dogs to retract,

means urging said movable means toward dog ing position,

pressure responsive means for moving said movable means toward dog retracting position,

and means holding said dogs in retracted position when said valve stem is not in position to bring the dogs into register with said grooves.

said valve including pressure responsive surfaces and extendmovable toward unseated position in response to pressure internal of said tubing which is greater than pressure external of said tubing and toward seated position in response to pressure external of said tubing which is greater than pressure internal of said 5 tubing when said dogs are in their retracted position 14. Method of unloading and Working a Well through a plurality of unloading valves which open in response to tubing pressure and close in response to casing pressure and which are set to close at decreasing casing pressures in descending order comprising,

introducing gas into the well casing at a rate which is less than the flow rate through the lowerrnost unloading valve and greater than the ow rate through 15 one unloading valve but less than the dlow rate through a plurality of unloading valves except the lowerniost unloading valve to unload the Well,

monitoring the casing pressure to observe pressure drops indicating closing of each unloading valve,

and after the well is unloaded increasing casing pressure to gas lift the well through a working valve at a pressure greater than the closing pressure of the lowerrnost unloading valve.

1S. Method of unloading and working a well through a plurality of unloading valves which open in response to tubing pressure and close in response to casing pressure and which are set to close at decreasing pressure in descending order comprising,

introducing gas into the Well casing at a rate which is less than the flow rate through the lowermost unloading valve and greater than the flow rate through one unloading valve but less than the flow rate through two unloading valves excepting the lowermost valve to unload the well,

monitoring the casing pressure to observe pressure drops indicating closing of each unloading valve,

and after the Well is unloaded increasing casing pressure to gas lift the Well through a Working valve at a pressure greater than the closing pressure of the lowermost unloading valve.

References Cited UNITED STATES PATENTS 2,673,707 3/ 1954 McRae 251-73 3,059,581 10/ 1962 Coberly et al. 251--73 X 3,082,785 3/1963 Radway 251-73 X 3,213,806 10/1965 Walton 137-155 X 3,272,226 9/ 1966 Dunlop et al 251--73 3,334,690 8/ 1967 Garrett 103-233 X FOREIGN PATENTS 1,024,765 2/ 1958 Germany.

DONLEY J. STOCKING, Primary Examiner.

W. I. KRAUSS, Assistant Examiner. 

1. A GAS LIFT SYSTEM COMPRISING, A CASING, A TUBING IN THE CASING, MEANS FOR SUPPLYING GAS TO THE CASING AT A CONTROLLED RATE, AND A PLURALITY OF UNLOADING VALVES AT SPACED INTERVALS ALONG THE TUBING; SAID VALVES INCLUDING, A MAIN VALVE MEMBER AND VALVE SEAT, MEANS RESPONSIVE TO ONE OF TUBING AND CASING PRESSURE FOR MOVING THE VALVE MEMBER TO OPEN POSITION, 